The present invention relates to a large-volume reactor of the type used for polymer production, specifically for mixing, reacting, degassing, and devolatilization of viscous solutions and melts, and free flowing materials.
Such large-volume reactors are commonly used in particular in the production and processing of polymers and plastics, and they usually have an interior space with a minimum volume of approximately 3 to 50,000 liters and a normal volume of approximately 1,000 to 20,000 liters. They are designed to ensure good mixing and kneading action over a broad viscosity range and therefore rapid renewal of the free surface.
A large-volume reactor of this type is disclosed, for example, in EP-A-1101525. EP-A-1101525 relates to a reactor with two shafts which are arranged parallel to one another and bear a number of rotating elements which extend as close as possible to the inner wall of the housing and to the shank of the opposite shaft and intermesh with one another.
Further large-volume reactors are described in EP-B-460466, EP-B-528210, EP-B-638354, EP-B-715881, EP-B-715882, EP-B-798093, EP-B-917941, EP-B-930141 and EP-A-1000657. A common feature of the known large-volume reactors is that they have an interior space surrounded by a housing, and therefore the material which is to be processed in the reactor is under the same pressure.
Many processes, such as for example concentration, degassing, devolatilization drying or polymerization processes, are very crucially dependent on the pressure in the process space. In processes of this type, it is advantageous to match the pressure to the physical and/or chemical materials properties in the process space, which change as the process continues.
By way of example, when devolatilizing material it is advantageous to devolatilize the volatile components (known as vapors) at more than one pressure, since the devolatilization at a single pressure would cause the entire quantity of vapors to be produced in a single stage, and this quantity could only be extracted and condensed by means of expensive vacuum installations and condensation systems.
Moreover, the high vapor velocity associated with the devolatilization at a single pressure would cause a relatively high proportion of the material to be entrained during separation of the vapors, which could cause considerable foaming in the material which is to be devolatilized and this would additionally have an adverse effect on the devolatilization process and could lead to undesirable deposits at the vapor outlet.
For processes carried out using known reactors, a plurality of pressures are established by virtue of the fact that a plurality of process spaces surrounded by separate housings—i.e. a plurality of small-space and/or large-space reactors—in which the appropriate pressure is present are arranged in succession and are connected to one another by means of pipelines.
EP-B 0768155 describes a process for producing polymer granules from a polymer solution in two individual reactors, in which the polymer solution is heated in a dwell tube or heat exchanger, which forms a first reactor, to a given temperature under a pressure of 1 to 15 bar, and the concentrated polymer solution is concentrated further at a given temperature and a pressure of 1 mbar to 5 bar in a drying apparatus which acts as a second large-volume reactor. Said drying apparatus comprises a material feed at one end of the housing and a material discharge at the other end of the housing, two rotor shafts, which convey the material in the direction from the material feed to the material discharge, being arranged in the interior space.
Reactor systems of this type have the drawback that, on account of their complex design, it is difficult to achieve operationally reliable passage of the material from one process space to another without harming the product. This is the case in particular if high-viscosity material is being conveyed, if high temperatures have to be set or if short residence times for the transfer are desired. In addition, said reactor systems take up an extremely large amount of space, since each individual pressure is assigned a process space surrounded by a separate housing. Therefore, reactor systems of this type entail high procurement, installation and maintenance costs.
The present invention is based on the object of providing a large-volume reactor having an interior space which is surrounded by a housing and in which different pressures can be established simultaneously.